Semiconductor power diodes typically include an anode, a cathode and a drift region between the anode and the cathode. Switching losses of power semiconductor diodes are mainly caused by charges which are stored during on-state and which must be removed when bringing the diode into the blocking state. The stored charges, sometimes also referred to as flooding charge, are desired during on-state since they reduce the so-called on-state resistance RON. The amount of the stored charge is mainly determined by the injection efficiency of the anode, injection efficiency of the cathode and the ambipolar lifetime of the charge carriers in the drift region.
There are several attempts to optimise these parameters for example by providing special doping profiles for the anode and the cathode to adjust the lifetime of the charge carriers, for example to limit their lifetime. However, there are constrains for the maximum concentration of recombination centres since a high amount of recombination centres leads to a high leakage current.
When considering the cathode efficiency, a reduction of the doping concentration is desired which, on the other hand, increase the on-state resistance. Further attempts include local adjustment of the lifetime of the charge carriers. The cathode can further include n-doped regions in contact with p-regions which are arranged between the n-doped regions and the drift region to reduce the flooding of the drift region by charge carriers during on-state.
While these and other attempts partially improve the switching behaviour of diodes, there is still need for further improvement.